This topic contains the following sections:

Availability, scalability, and clustering technologies

Windows Server® 2008 provides two clustering technologies: failover clusters and Network Load Balancing (NLB). Failover clusters primarily provide high availability; Network Load Balancing provides scalability and at the same time helps increase availability of Web-based services.

Your choice of cluster technologies (failover clusters or Network Load Balancing) depends primarily on whether the applications you run have long-running in-memory state:

  • Failover clusters are designed for applications that have long-running in-memory state, or that have large, frequently updated data states. These are called stateful applications, and they include database applications and messaging applications. Typical uses for failover clusters include file servers, print servers, database servers, and messaging servers.

  • Network Load Balancing is intended for applications that do not have long-running in-memory state. These are called stateless applications. A stateless application treats each client request as an independent operation, and therefore it can load-balance each request independently. Stateless applications often have read-only data or data that changes infrequently. Front-end Web servers, virtual private networks (VPNs), File Transfer Protocol (FTP) servers, and firewall and proxy servers typically use Network Load Balancing. Network Load Balancing clusters can also support other TCP- or UDP-based services and applications.

Failover cluster overview

By using a failover cluster, you can ensure that users have nearly constant access to important server-based resources. A failover cluster is a set of independent computers that work together to increase the availability of services and applications. The clustered servers (called nodes) are connected by physical cables and by software. If one of the nodes fails, another node begins to provide service through a process known as failover.

You can use the Failover Cluster Manager snap-in to validate failover cluster configurations, create and manage failover clusters, and migrate some resource settings to a cluster running Windows Server 2008 R2.

In Windows Server 2008, the changes to failover clusters (formerly known as server clusters) are aimed at simplifying cluster setup and management, making the clusters more secure and stable, improving networking in clusters, and improving how failover clusters communicate with storage.

What are failover clusters?

A failover cluster is a group of independent servers that are running Windows Server 2008 and working together to increase the availability of services and applications. When a failure occurs on one computer in a cluster, resources are redirected and the workload is redistributed to another computer in the cluster. You can use failover clusters to ensure that users have nearly constant access to important server-based resources.

Hardware and software considerations for failover clusters


A limited set of server roles is available for the Server Core installation option of Windows Server 2008 and for Windows Server 2008 for Itanium-Based Systems.

Microsoft supports a failover cluster solution only if all the hardware components are marked as "Certified for Windows Server 2008 R2." In addition, the complete configuration (servers, network, and storage) must pass all tests in the Validate a Configuration Wizard, which is included in the Failover Cluster Manager snap-in.

The software used for managing a failover cluster is the Failover Cluster Manager snap-in, which is installed as part of the failover cluster feature in Windows Server 2008 R2. The underlying service that supports failover clusters is the Cluster service.

Installing the failover cluster feature

Use Initial Configuration Tasks or Server Manager to install features. To install the failover cluster feature:

  1. In the list of tasks, click Add features.

  2. In the list of features presented in the wizard, click Failover Clustering.

Managing a failover cluster

Server roles and features are managed by using Microsoft Management Console (MMC) snap-ins. To open the failover cluster snap-in, click Start, click Administrative Tools, and then click Failover Cluster Manager.

Additional references for failover clustering

To learn more about failover clusters, you can view the Help on your server. To do this, open the failover cluster snap-in as described in the previous section, and then press F1.

For more information about failover clusters, see the following resources on the Microsoft Web site: